Pressure balanced percussion firing system

ABSTRACT

Percussion firing apparatus for firing an explosive charge in a downhole tool without using an electrical system characterized by a chamber and a pressure balancing piston and including a percussion firing head assembly that is set in the well and, on a subsequent trip, a firing prong employed to move the pressure balancing piston downwardly to arm and ultimately fire via a firing pin a charge. After the charge is fired the entire percussion firing apparatus is pulled from the well. The apparatus provides consistent firing regardless of internal and external pressures of variations therein, or of the fluids in the well. Also disclosed are positive safety features; such as, running the percussion firing head assembly with the firing pin disarmed, and a single-fire safety construction that allows only one firing attempt; as well as other advantageous features and specific structure and assembly.

United States Patent [1 1 Tamplen 1 PRESSURE BALANCED PERCUSSION FIRHNGSYSTEM Jack W. Tamplen, RR. 2, Celina, Tex. 75009 22 Filed: Mar. 30,11973 [21] Appl. No.: 347,324

[76] Inventor:

Primary Examiner-Verlin R. Pendegrass Attorney, Agent, or Firm-Wofford,Felsman & Fails 1 1 Apr. 2, 1974 [57] ABSTRACT Percussion firingapparatus for firing an explosive charge in a downhole tool withoutusing an electrical system characterized by a chamber and a pressurebalancing piston and including a percussion firing head assembly that isset in the well and, on a subsequent trip, a firing prong employed tomove the pressure balancing piston downwardly to arm and ultimately firevia a firing pin a charge. After the charge is fired the entirepercussion firing apparatus is pulled from the well. The apparatusprovides consistent firing regard less of internal and external pressures of variations therein, or of the fluids in the well. Alsodisclosed are positive safety features; such as, running the percussionfiring head assembly with the firing pin disarmed, and a single-firesafety construction that allows only one firing attempt; as well asother advantageous features and specific structure and assembly.

38 Claims, 7 Drawing Figures MTENYEU APR 2 I974 SHEET 2 UP 2 PRESSUREBALANCED PERCUSSION FIRING SYSTEM BACKGROUND OF THE INVENTION 1. Fieldof the Invention This invention relates to subsurface well apparatus;and, more particularly, to percussion firing apparatus for firing anexplosive charge within a wellbore penetrating subterranean formations.

2. Description of the Prior Art The prior art has seen the developmentof a wide va riety of apparatus for firing explosive charges downhole ina well penetrating subterranean formations; including firing by wirelines. Such charges were used in' a wide variety of applications. Forexample, setting tools were operated with such charges to set bridgeplugs and/or packers; perforating guns were employed to effectcommunication between the interior of a conduit in a well and thesubterranean formations penetrated by the well; and explosive cut-offtools were employed to sever sections of conduit or the like. Primarily,the apparatus for firing an explosive charge has developed along thelines of either electrically fired systems or thenonelectrical systemsthat resorted to percussion firing of an igniter. The electrically firedsystems require care in connection, handling and transportation, as wellas in running; since the electrical systems are subject to straycurrents, as from radio frequency transmission towers, staticelectricity, and the like. Such electrically fired systems are alsogenerally more expensive in operation and are not as readily availablein the field as are the nonelectrical wire line units. The percussionfiring systems, on the other hand, have required care in handling andhave been dangerous because of the danger of an inadvertent bloweffecting firing of the charge, either during handling or while beinglowered into the well. Moreover, the prior art percussion firingapparatus has been dangerous and unsatisfactory because it could not beascertained with certainty that it had been fired or disarmed in thewellbore, so that it was risky to go in and retrieve the percussionfiring assembly. Expressed otherwise, a sharp blow during the retrievaloperation could cause inadvertent firing, sometimes at the incorrectdepth with resultant damage to the well casing or conduit. it will beapparent that such inadvertent firing, when the charge is properlylocated at the correct depth, is not necessarily disadvantageous, sincesuch firing would still achieve the desired result. ln my U.S. Pat. No.3,710,717, entitled PERCUSSION FIRING SYSTEM, 1 described an improvedapparatus that obviated the disadvantages of the prior art. Good as thatimproved percussion firing system was, however, it still did not afforda completely satisfactory system that had the desirable featuresdelineated hereinafter.

It has been found that, when running explosives to extreme depths inhigh pressure oil wells, external pressures attempting to enter theexplosive chamber is very high; and, on the other hand, when theexplosives are ignited, the internal pressures sometimes becomeextremely high even in the firing pin chamber. The prior art hasprovided an external firing system which requires a reinforcing discplus extemely close fits between the parts to prevent the externalpressure from deforming the top of the primer shell. Also, when theexplosives were ignited, the reinforcing discs would often be blown outpermitting the internal pressure to bleed off without completelyoperating the attached device, such as a pressure setting tool 13.Moreover. the thickness of the reinforcing disc often made it impossiblefor the firing pin to penetrate the reinforcing disc sufficiently toobtain ignition of the igniter means. Sand, pipe scale, and even heavymuds also adversely affected the chances for success of obtaining firingwith an external firing mechanism.

Experience had indicated that a percussion firing apparatus for firingan explosive charge within a well penetrating subterranean formationsshould have the following features.

I. The percussion firing head assembly should be firable by a directforce and not require speed, thereby:

a. enabling being fired by either wire line, a tubing string, ordropping a sinker bar from the surface; and

b. enabling operation at great depth and in viscous fluids in thewellbore.

2. The percussion firing head assembly should have its arming, firingand safety mechanism contained inside an enclosed firing chamber so asto not be adversely affected by sand, pipe scale, or well fluids.

3. The percussion firing head assembly should have a pressure balancingmeans to prevent external pressure or internal pressure or suddenchanges in these pressures from affecting the downhole arming and firingsequences.

4. The percussion firing head assembly should include an armingmechanism that is run and set in the unarmed condition.

5. The arming mechanism should inlcude releaseable retainer means thatmust be overcome before the arming sequence can begin.

6. A second releasable retainer means should be included as anadditional safety factor to prevent firing before it is overcome.

7. A means should be provided for retaining pressure within thepercussion firing head assembly to ensure operation of an attached tool,such as a pressure setting tool, in the event there is a bleeding off,or blow-by," of pressure past the firing pin assembly. In this wayoperation of the tool is ensured even if there is blowby of fluids, orgases from fired charges.

8. It is desirable that ignition be facilitated by omission ofinterfering elements between the firing pin and the igniter and with theigniter insulated from wellbore pressure and fluids. This enablesemploying less sensitive and less expensive ignition caps.

9. The load delivered to the firing pin should be consistent, andinvariant for each run, regardless of well conditions, to ensure firingwithout piercing completely through the firing cap.

10. The arming and firing assembly should be disarmed after one firingattempt for safety in subsequently handling the tools in the event of amirfire.

l l. The firing pin should have a supplemental safety feature to ensureadequate pentration for ignition but to prevent subsequent ignition inthe event of a misfire.

12. The percussion firing head assembly should be adaptable to beemployed with either an internal fishing neck or an external fishingneck. 13. The percussion firing head assembly should be adapted to befired by an inexpensive one-piece firing prong used on a second trip toarm and fire the charge while the percussion firing head assembly isretained, or hung, at a given depth in the wellbore.

14. The percussion firing head assembly, the onepiece prong describedimmediately hereinbefore, and the associated pulling tool should bedesigned such that the pulling tool engages the percussion firing headassembly fishing neck before ignition occurs to prevent dropping of thefiring head assembly in cases where the explosives move the pulling tooland the percussion firing head assembly up the borehole sufficiently toloosen the slips during ignition.

Accordingly, it is an object of this invention to provide a percussionfiring apparatus having an internally contained firing mechanism thatobviates the disadvantages of the prior art delineated hereinbefore, andhaving an additional one or more of the desirable features delineatedhereinbefore and not heretofore provided.

It is another object of this invention to provide a percussion firingapparatus for firing an explosive charge within a well penetratingsubterranean formations in which the apparatus has all of the desirablefeatures delineated hereinbefore.

These and other specific objects will be apparent from the followingdescriptive matter when taken in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a schematic elevational viewof one embodiment of this invention in a wire line tool string, the toolstring being shown within a cased wellbore.

FIG. 2 is a fragmentary longitudinal sectional view of the upper part ofthe percussion firing head assembly of FIG. 1.

FIG. 3 is a fragmentary longitudinal sectional view of the middle partof the percussion firing head assembly of FIG. 1.

FIG. 4 is a fragmentary longitudinal sectional view of the bottom partof the percussion firing head assembly of FIG. I.

FIG. 5 is a fragmentary longitudinal sectional view of the percussionfiring head assembly of FIG. 2 with a firing prong being employed toeffect the arming and firing of the firing pin therewithin.

FIG. 6 is a schematic view of an unfolded exterior of the bodyillustrated in FIG. 3; showing the J-slot arrangement for controllingthe means for setting the slips.

FIG. 7 is a partial side elevational view, partly in section, of anembodiment of this invention employing an external fish neck.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring to the drawings, FIG. 1illustrates a percussion firing head assembly 11, a setting tool 13 anda bridge plug 15, all of which are removably attached to a running tool17 and suspended by a tool string 19 from a non-electrical wire line 21in a section of conduit 23, such as casing, in a cased wellbore 25. Theelements other than the percussion firing head assembly II areconventional and need not be described in detail herein. For example,the bridge plug and the setting tool 13 are described in US. Pat. Nos.3,l8(i,485 and 3,266,575, issued to H.D. ()wen. It is sufficient to notthat when an explosive charge within the setting tool 13 is fired, thebridge plug is set in the conduit 23 by the 4 setting tool; and thesetting tool 13 thereafter shears a shear pin to separate from thebridge plug 15. The setting tool 13 may then be pulled from the wellbore25.

The setting tool 13 may be fired in response to the firing of anexplosive charge, such as the igniter means in the percussion firinghead assembly 11.

As illustrated, the percussion firing head assembly 11, with a settingtool 13 and the bridge plug 15 attached thereto, is being emplaced at apredetermined depth in the wellbore 25 with a shear down" running tool.Such shear down" running tools are conventional and have thecharacteristic that when jarred downwardly to produce a large force, ashear pin is sheared to release the tool from a device with which it isconnected, such as the percussion firing head assembly 11. Conversely, ashear up tool has the char acteristic that it will shear a shear pin andrelease any device with which it is connected when a sufficiently largeupwardly acting force is developed, as by being jarred upwardly. Sheardown running tools and shear up" pulling tools are employedconventionally with a tool string that has means such as jars fordeveloping upwardly and downwardly acting forces. Moreover, the runningand pulling tools have means for engaging the fishing neck means of thepercussion firing head assembly 11. After the percussion firing headassembly 11 is emplaced in the conduit 23, a firing prong 26, FIG. 5, isinserted on a second trip and the explosive charge fired to actuated thesetting tool and set the bridge plug in place. After the bridge plug isset, the setting tool is sheared off and pulled from the wellbore 25;and the bridge plug is left in the well. If the setting tool 13 fails toshear completely free of the bridge plug 15, it may be sheared therefromby a jarring force transmitted through the shear up pulling tool becauseof the preselected relative sizes of the respective shear pins.

Referring to FIGS. 2-4, the percussion firing head assembly 11 comprisespressure balancing means 27 for neutralizing the adverse effects ofexternal pressure and internal pressure and transients, or changes,therein; firing pin assembly 29; igniter means 31; settable hangingmeans 33; and first connection means 35.

The pressure balancing means 27 includes a chamber 37 and a pressurebalancing piston 39. The chamber 37 has an enlarged annular passageway41 that opens at its bottom end to facilitate insertion of the pressurebalancing piston 39. A plurality of ports 43 communicate intermediatethe interior of the chamber 37 and the exterior of the outer housing 45of the percussion firing head assembly 1 l. The outer housing 45 has aninternal thread 47 for conformingly and sealingly receiving an externalthread 49 of a second and lower housing section 51.

The pressure balancing piston 39 has a lower end 53 that is adapted toengage the upper end 55 of the hammer pin 57, described in more detailhereinafter with respect to the arming means of the firing pin assembly.The pressure balancing piston 39 has an upwardly extending member 59that has adequate structural strength for pushing the pressure balancingpiston 39 downwardly for arming and firing. The upwardly extendingmember 59 protrudes into the prong receiving chamber M for a length L,that is suflicient to move the pressure balancing piston 39 downwardlysufficiently to arm and fire the firing pin assembly 29 and ignitermeans'3l. Specifically, the length L, is greater than the distanceseparating the lower end 53 of the pressure balancing piston 39 and theupper end 55 of the hammer pin 57 to ensure that positive contact ismade between the pressure balancing piston 39 and the hammer pin 57 forthe arming and firing operation. The upwardly extending member 59 isdisposed in and movable reciprocally of a first longitudinally extendingbore 63. The upwardly extending member has a first cross sectional area,or first area, 65. As illustrated, the upwardly extending member 59 iscylindrical in shape. Suitable seal means, such as o-rings 67, sealinglyengage the upwardly extending member 59 and the internal walls of thebore 63 to seal against flow of fluids therepast. Any pressure onthe'respective sides of the piston, therefore, will act against thefirst area 65.

As illustrated, the outer housing 45 has downwardly and outwardlyextending passageways 69 for draining off sand and other types of debristo ensure that a firing prong can be admitted into the firing prongreceiving chamber 61. Consequently, the first area 65 is exposed to thepressure of the borehole fluids, creating a downward force on thepressure balancing piston 39.

In order to balance this force, the pressure balancing piston 39 has alarge central portion 71 disposed in the chamber 37. As illustrated, thelarge central portion 71 is cylindrical in shape and has the samediameter as the chamber 37 so as to effect a second cross sectionalarea, or second area, 73. Suitable seal means, such as o-rings 75,sealingly engage the large central portion 71 and internal walls of thechamber 37 so as to maintain a seal therebetween as the large centralportion 71 is moved longitudinally of the chamber 37. Pressure balancingpiston 39 has a lower portion 77 that is slidably disposed in alongitudinal bore 79 of the second housing section 51. The lower portion77 has a third cross sectional area, or third area, 81. As illustrated,the lower portion 77 is also cylindrical in shape. Suitable seals, suchas O-rings 83, sealingly engage the lower portion 77 and the internalwalls of the longitudinal bore 79 to maintain a seal as the lowerportion 77 is moved longitudinally of the bore 79. Thus, it can be seenthat the external pressure of the borehole fluids will enter via ports43 and act against the exposed surface" of the large central portion 71.The exposed surface is the difference between the second area 73 and thethird area 81. The exposed surface is made such that it equals the firstarea 65. Consequently, the external pressure acting on the exposedsurface of the large central portion 71 will cancel out and oppose thepressure acting on the first area 65, balancing the force of theexternal pressure on the pressure balancing piston. Consequently, thepiston does not move; even though the external pressures may become veryhigh as a tool is lowered into a wellbore having aqueous based fluidstherein.

The pressure balancing piston 39 has a central longitudinally extendingbore 87 with branch passageways 89 that communicate with the top portionof the chamber 37. Consequently, the internal pressure within thelongitudinal bore 79 acts on the third area 81, either at the lower end53 or at the top 91, with a third force. The difference between thesecond area 73 and the third area 81 is also chosen to be the same asthe third area 81 such that the internal pressure will also act on thelarge central portion 71 to generate a fourth force that opposes andcancels out the third force. As a result, the pressure balancing piston39 is again at pressure equilibrium and does not move as a result ofinternal pressure either, regardless of whether the internal pressure isless than or greater than the external pressure. As will be appreciated,the internal pressure will normally be at about atmospheric pressurewhen the tool is being run into the well, by may become very highfollowing the ignition of the charges if there is sufficient blow-by ofgases past the firing pin 93 of the firing pin assembly 29. Thus, thepressure balancing piston 39 does not move responsive to pressure, butmoves responsive to an external force imposed upon it. This externalforce may be supplied by any of the means described herein, or any othersuitable means.

Moreover, the pressure balancing piston 39, with its seal means,prevents communication between the interior of the percussion firinghead assembly 11 and the exterior thereof, both before and after firing;with the numerous advantages delineated herein.

A releasable piston retainer means is employed to prevent prematuremovement, or creep, of the pressure balancing piston 39 until a force isapplied to fire the igniter means 31. The piston retainer meanscomprises a shear pin ring 113 disposed about the lower portion 77 ofthe pressure balancing piston 39. The shear pin ring 113 is slidablelongitudinally of the lower portion 77, but is releasably connectedtherewith by shear pins 1 15. As illustrated, two shear pins arediametrically opposed for balanced retention and to afford a balancedforce when they are sheared by downward movement of the pressurebalancing piston 39. The shear pin ring 113 encounters the top 116 ofthe second housing section 51 to limit its downward travel for shearingof the shear pins 115.

The firing is accomplished with the firing pin assembly 29. The firingpin assembly 29 comprises the firing pin 93 disposed therewithin and anarming means 94 for arming and firing. The arming means 94 is disposedintermediate the firing pin 93 and the pressure balancing piston 39 suchthat the firing pin ultimately can be forced sharply downwardly by adownward force on the pressure balancing piston 39.

The firing pin 93 has an enlarged head 95 designed for being repeatedlystruck by the hammer pin 57. To prevent the firing pin 93 from beingblown up the bore and out of position in the event the igniter means 31disintegrates, a threaded enlarged portion 97 is screwed throughthreaded aperture 99 of a hammer pin retainer 101 so as to be slidablydisposed within bore 103 of the firing pin retainer 105. Suitable sealmeans, such as O-ring 106, sealingly engage the firing pin retainer 105and the walls of the bore into which it is inserted within the lower endof the second housing section 51. As illustrated, the firing pin 93 hasa controlled penetrating depth safety feature that assures the adequatepenetration for ignition but acts as a safety feature in the unlikelyevent of a misfire, or failure of the igniter means 31 to fire.Specifically, the controlled penetrating depth firing pin can berepeatedly knocked to the same depth without firing the igniter means 31if the firing pin 93 fails to fire the igniter means 31 the first time.Moreover, the controlled depth firing pin prevents penetratingcompletely through the upper sur face of the igniter means 31 andlessens the chances of blow out of the igniter means. In the controlledpenetrating depth safety feature, the bottom of the enlarged head 95encounters the top surface of the bottom of the hammer pin retainer 101to limit the downward movement of the firing pin 93. If desired, thecontrolled penetrating depth safety feature may comprise a first annularshoulder 107 dispoed annularly of the small lower end 109 of the firingpin, and a mating second annular shoulder 111 extending concentricallyinteriorly of the bore 103. Thus, when the first annular shoulder 107encounters the second annular shoulder 111, downward movement of thefiring pin is stopped. The depth penetration is thereby controlled,during and after firing; which, of course, follows the arming by thearming means 94.

The arming means 94 includes the hammer pin 57 disposed intermediate thefiring pin assembly 29 and the pressure balancing piston 39. The upperend 55 of the hammer pin 57 has a slot 124 that allows fluid to flow,even ifthe upper end 55 engages the lower end 53 of the pressurebalancing piston 39. The arming means 94 also includes a releasablehammer pin retainer means; such as, shear pin 117 in hammer pinretainer, or skirt, 101; and a biasing means, such as spring 1 19.

As illustrated, the shear pin 117 penetrates through matching aperturesin the hammer pin 57 and the hammer pin skirt 101 and serves twopurposes. First, it serves as a releasable retainer means to retain thehammer pin in its top position until a sufficient force has beengenerated by the downward movement of the pressure balancing piston 39.The sufficient force is that which is great enough to compress thespring 119 a predetermined amount, effect solid contact between thelower end 53 of the pressure balancing piston 39 and the top 55 of thehammer pin 57, and shear the shear pin 117. Second, it, in combinationwith the hammer pin skirt 101, forms a single-fire safety. Expressedotherwise, the single-fire safety retains the hammer pin 57 in its topposition preparatory to firing, so that it can be snapped downwardlylongitudinally of the hammer pin skirt 101 for firing only one time. Asillustrated, the hammer pin 57 is cylindrical. The hammer pin skirt 101comprises a cylindrical tubular skirt that engages the firing pinretainer 105 for affording a positive retaining and stopping force. Thehammer pin skirt 101 has a top portion that closely fits the exterior ofthe bottom of the hammer pin 57. An enlarged bore 104 prevents anydragging or fluid compression effects and allows free and rapid downwardmovement of the hammer pin 57 once the shear pin 117 is sheared. Thehammer pin skirt 101 has a downwardly and inwardly depending portioncontaining the threaded aperture 99 through which the firing pin 93 isinserted, as described hereinbefore.

The spring 119 is provided to afford a constant and reproduceable firingforce each time firing is attempted, regardless of the pressureexternally of the percussion firing head assembly 11. Specifically, thespring 119 is not initially compressed, but is compressed by downwardmovement of the pressure balancing piston 39 to store the constant andreproduceable amount of force before the lower end 53 of the pressurebalancing piston 39 contacts the upper end 55 of the hammer pin 57.After contact, a greater force is generated to shear the shear pin 117.Once the shear pin 117 is sheared, the hammer pin 57 moves rapidlydownwardly to strike the firing pin 93 and ignite the igniter means 31.It is noteworthy that the hammer pin is accelerated by the constantforce stored in the spring 8 119, but relies upon inertia to strike thefiring pin 93. The bottom of the spring 119 is stopped before the hammerpin 57 strikes the firing pin 93, as will become apparent from thedescription of a supplemental safety feature hereinafter.

A supplemental safety feature is provided, in the event there is amisfire. The supplemental safety feature prevents any subsequentcompression of the spring 119 from moving the hammer pin 57 downwardlyonto the firing pin 93. The supplemental safety feature comprises anannularly disposed washer 121 disposed at the bottom of the spring 119and an interiorly protruding shoulder 123 of the hammer pin skirt 101.The washer 121 serves as a spring stop when it engages the shoulder 123.Specifically, the downwardly moving washer 121 will encounter theinteriorly protruding shoulder 123 and prevent further'downward movementof the bottom end of the spring 119. Thus, even though the pressurebalancing piston 39 may creep a little after the first firing attempthas been made, and put a small compressing force on the spring 1 19, theforce cannot be transmitted downwardly onto the hammer pin 57 forsubsequent downward movement of the firing pin 93.

From the foregoing, it can be seen that the arming means 94 is unarmedduring running. It remains unarmed until after the percussion firinghead assembly 11 is set in the conduit 23 is the wellbore 25; and thearming and firing attempt is made. Moreover, after the firing attempthas been made, the arming means is also disarmed so as to prevent anyfurther firing attempts to be inadvertently made, as sometimesundesirably happens with conventional apparatus and igniter means.

The igniter means 31 comprises a small explosive charge, such as igniter127; and is disposed beneath the firing pin 93 so as to be ignitedresponsive to a downwardly moved firing pin 93. One of the advantages ofthis invention is that no safety disc is required to be dis posed abovethe igniter 127, either to prevent its firing or to prevent upwardmovement of gases from diminishing the power ofa setting tool or thelike in the event that the igniter 127 disintegrates. As illustrated,the igniter 127 has an upper flange 129 that is received in a removableejector cap 131. The ejector cap 13l,is ,disposed on top ofa receiver133 that carries the igniter 127. The ejector cap 131 will pull theigniter 127 from the receiver 133 when the ejector cap 131 is liftedfrom the top of the receiver 133. This provides a convenient way ofremoving the igniters 127 and provides another safety factor when amisfiring of an igniter has occured. As is recognized, rodding from thebottom, as would otherwise be necessary, is dangerous. The ejector cap131 is received in a recess in the lower end of the second housingsection 51. The second housing section 51 is removably connected, as bythreaded connection 135, with the receiver 133 for retaining the ejectorcap 131 in place. As can be seen, the top of the ejector cap 131 abutsthe bottom of the firing pin retainer 105. The igniter means 31 has apercussion cap 137 to initiate firing responsive to a sharp downwardforce by a small lower end 109 of the firing pin 93. The arming andfiring is performed after the percussion firing head assembly 11 is set,or suspended, in the conduit 23.

The settable hanging means 33 is provided for suspending the percussionfiring head assembly 11 in the conduit 23. As illustrated, the settablehanging means comprises drag show means 139 and slip means 141.

The drag shoe means 139 are means for dragging on the walls of theconduit 23 so as to move the slip means to the maximum position allowedby a J-slot arrangement opposite the direction of movement of thepercussion firing head assembly 11 in the conduit. The slip means 141serve, as is well known, to removably jam into engagement with the innerwalls of the conduit 23 for immobilizing the percussion firing headassembly against a downward force from above.

The drag shoe means 139 contain a guide means, such as guide pin, orball, 143, that engages a J-slot arrangement 145, FIG. 6. The drag shoemeans 139 is otherwise freely movable reciprocally along a portion 147of the percussion firing head assembly 11. The guide ball 143 isretained in place by a band 149 that is rotatably disposed within thedrag shoe housing 151. The drag shoe means 139 has drag shoes 153 forfrictionally dragging on the walls of the conduit 23. The drag shoes 153have, at each end, an extending lip 155 that prevents their being pushedout of the drag shoe means 139 by the springs 157. The guide ball 143serves to limit the upward and downward movement of the drag shoe means139, depending upon which slot in the J-slot arrangement 145 it engages.The J-slot arrangement 145 and the guide ball 143 are conventional andallow an operator at the surface to control setting of the slip means141 by reciprocal movement of the percussion firing head assembly 11within the conduit 23, as will become more clearly apparent from theoperational description hereinafter.

As illustrated in unfolded format in FIG. 6, the .I-slot arrangement 145is cut peripherally around the portion 147. The .I-slot arrangement 145is continuous peripherally around the portion 147 for guiding the guideball 143 through repetitive traverses through 360 around the portion147. The .I-slot arrangement 145 has an entry slot 159 for entry of theguide ball 143 into the J-slot arrangement 145. The .I-slot arrangement145 also has an elongate upwardly extending slot 161 for allowing theguide ball 143 to move upwardly for setting the slip means 141.

The slip means 141, FIG. 3, are connected with the drag shoe means 139so as to be moved upwardly and downwardly responsive to the respectivemovement of the drag shoe means 139. Expressed otherwise, the drag shoe153 frictionally drag on the walls of the conduit 23 and bias, throughtheir frictional force, the drag shoe means 139 upwardly or downwardlyas the tool is moved respectively downwardly or upwardly. The slip means141 follow the movement of the drag shoe means 139. An inverted conemeans, such as cone 163, is disposed adjacent the slip means 141 whenthe slip means 141 are at their lower point. The inverted cone 163 isadapted for upward travel of the slip means 141 thereon for extension ofthe slip means 141 outwardly to engage the walls of the conduit 23 forsetting a percussion firing head assembly 11. Expressed otherwise, theslip means 141 are set, or engaged with the conduit 23, by downwardmovement of the percussion firing head assembly 11 when the guide ball143 is in the upwardly extending slot 161, FIG. 6, allowing the slipmeans 141 to run up on the inverted cone 163. The slip means 141 aremore rigidly set by a greater downward force. Conversely, the slip means141 are released by an upward force on the percussion firing headassembly 11 sufficient to pull the inverted cone 163 from beneath theslip means 141.

The first connection means 35, FIG. 4, is provided for connection with adevice that is actuated responsive to firing of the igniter means 31. Asillustrated, the first connection means 35 comprises a male thread of athreaded connection for joining to a female thread on the device that isto be actuated.

Ordinarily, it will be advantageous to provide a percussion firing headassembly 11 with a fishing neck means 167 for connection with a runningand pulling tool. The fishing neck means 167 may comprise either aninternal or an external fish neck. The fishing neck means 167 isdisposed at the upper end of the percussion firing head assembly 11. Asillustrated, the fishing neck means 167 comprises an internal fishingneck means that is adapted for being suspended from a running or apulling tool equipped for such internal fish necks. Specifically, thefishing neck means 167 is adapted for being suspended from a shear downrunning tool and for being engaged and pulled upwardly by a shear uppulling tool.

A prong receiving chamber 61 is disposed adjacent the fishing neck means167 and is adapted for receiving a firing prong 26, as illustrated inFIG. 5. The prong receiving chamber has a length sufficient to receivethe prong 26 therewithin and th ensure that the dogs 169 ofa pullingtool 171 will engage the interiorly protruding annular ring 173 of theinternal fish neck before the igniter means 31 is fired. The fishingneck means 167 is disposed in the fishing neck sub 177. The fishing necksub 177 forms a housing defining the prongreceiving chamber 61 and isthreadedly connected by a threaded connection 179 with the lower sub, orouter housing, 45.

It has been found advantageous to emplace the igniter means 31 at theupper portion of the percussion firing head assembly for a top firingtool. An elongate detonation passageway 181, FIGS. 2-4, is disposedintermediate the igniter means 31 and the first connection means 35 fordownward passage of the shock wave from the ignition of the igniter 127.When an elongate detonation passageway 181 is employed, it is frequentlypreferably to also employ a shooting adapter 183 at the lower end of thedetonation passageway, FIG. 4. The shooting adapter 183 has a thirdconnection means, such as threads 185, for connection with a device tobe actuated in response to ignition of the booster pellet 187. Thebooster pellet 187 increases the likelihood that the device that is tobe actuated will be actuated in response to ignition of the igniter 127.

If desired, an elongate prong receiving chamber 61 and elongate firingprong 26 could be employed and eliminate the necessity for thedetonation passageway 181. On the other hand, an elongate upwardlyextending member 59 can be employed and eliminate the necessity for anelongate prong.

The overall operation has been described hereinbefore with respect toFIG. 1. Detailed considerations will now be described. Assume that thepercussion firing head assembly 11 has been assembled as illustrated inFIGS. 2-4 except that the guide ball 143, instead of being at the upperposition 189, FIG. 6, is disposed at the lower position 191 and the slipmeans 141 are below the inverted cone 163, FIG. 3. A running tool 17 isattached to the fishing neck means 167 and the percussion firing headassembly 11 is run into the wellbore 25. As the percussion firing headassembly 11 moves downwardly in the conduit 23, the drag shoe means 139tend to move upwardly, moving the guide ball 143 to the top 193 of therunning slot 195. The running slot 195 maintains the slip means 141 in aposition below the inverted cone 163. The path the guide ball 143follows in the J-slot to reach the top 193 is indicated by the arrows197. As indicated hereinbefore, the J-slot is relatively conventionaland need not be described in detail herein. The running slot 195 and thepreparatory slot 199 are somewhat elongated in order to allow forvariations in speed in the wellbore and to keep the guide pin in thedesired slot. When the desired depth has been reached, the running tool17 is stopped and pulled upwardly. The guide ball 143 is moved to thebottom 201 of the preparatory slot 199 by the relative downwardfrictional force of the drag shoes 153 against the conduit 23.Thereafter, the running tool 17 is again lowered. The drag shoe means139 move upwardly with respect to the percussion firing head assembly11, moving the guide ball 143 toward the upper position 189 in theupwardly extending slot 161, or as far as the slip means 141 will allowbefore they engage the walls of the conduit 23. Ordinarily, the slipmeans 141 will engage the conduit 23 before the guide ball 143 reachesthe upper position 189. Thus, the percussion firing head assembly 11 isset in the well. Further downward force merely serves to set it moretightly in the well. By pulling the percussion firing head assembly 11upwardly, however, the operator can release the slip means 141. Theoperator can safely set and release the slip means 141 as many times asnecessary to obtain the desired setting depth, since the arming means isnot armed and the igniter means 31 is protected from being fired by therespective first and second retainer means.

In fact, during running there are several safety factors that arenoteworthy in this invention. The pressure balancing piston 39 isprevented from accidentally moving until the shear pins 115 are shearedbetween it and the shear pin ring 113. Also, the spring 119 of thearming means is not compressed in the run-in position so the armingmeans is unarmed; but it is compressed only after the shear pins 115have been sheared and the balancing piston moved downwardly. Moreover,the hammer pin shear pin 117 cannot be sheared until the lower end ofthe pressure balancing piston 39 engages the upper end 55 of the hammerpin 57.

Once the percussion firing head assembly 11 is set, the shear downrunning tool 17 is jarred downwardly to shear its shear pin anddisengage the fishing neck means 167. The running tool 17 is thereafterpulled from the well.

At the surface a shear up" pulling tool 171 is attached to the toolstring 19; and a firing prong 26 is connected to the lower end of thepulling tool 171. The pulling tool 171 and the firing prong 26 are thenrun into the well. The firing prong 26 is run through the fishing neckmeans 167 and encounters the upwardly extending member 59 of thepressure balancing piston 39.

As the bottom 175 of the firing prong 26, or similar prong, lands on theupper end of the upwardly extending member 59, downward jarring; or, infact, any downward force of sufficient magnitude; will move the pressurebalancing piston 39, shear pin ring 113 and shear pins 115 downwardlyuntil the shear pin ring 113 encounters the top 116 of the secondhousing section 51. Further downward force or jarring will shear theshear pins 115, permitting the pressure balancing piston 39 to telescopedownwardly through the shear pin ring 113. Further downward movement ofthe pressure balancing piston 39 compresses the hammer pin spring 1 l9and brings the lower end 53 of the pressure balancing piston 39 intoengagement with the upper end 55 of the hammer pin 57. At this point,the hammer pin spring 119 is fully compressed to deliver a uniformacceleration to the hammer pin 57. Further downward force on thepressure balancing piston 39 will impose force onto the hammer pin 57and, ultimately, will shear shear pin 1 17. When the shear pin 1 17shears, the hammer pin 57 will be snapped downwardly onto the firing pin93, firing the igniter means 31.

A indicated hereinbefore, the dogs 169 on the pulling tool 171 will haveengaged the internal fishing neck ring 173 before the prong 26 andpressure balancing piston 31 have moved downwardly sufficiently to shearshear pin 117 and fire the igniter 127. The pulling tool engages theinternal fishing neck means 167 to retain the percussion firing headassembly 11 in place, even if there is sufficient upward movement toloosen the slip means 141 as a result of the firing of the setting toolor the like that is connected with the lower end of the percussionfiring head assembly 11.

Even if the igniter means is disintegrated so badly that there isblow-by of gases around the firing pin area, as may occur when usinghigh order explosives, the only pressure loss is the small volume of gasrequired to fill the chamber about the firing pin 93 and the bore 79.Escape exteriorly of the percussion firing head assembly 1 1 isprevented by the pressure balancing piston 39. The feature ensuresoperation of any pressure actuated tool that is appended to the lowerend of the percussion firing head assembly 11. Moreover, any increase inpressure as a result of firing and blow-by imposes a balanced force onthe pressure balancing piston 39 by reason of the opposed areasdescribed hereinbefore. Consequently, any blow-by or pressure build doesnot adversely affect any of the sequency of steps necessary to obtainignition or diminish the chances of obtaining ingition.

The additional safety feature of the washer 121 encountering theshoulder 123 to stop transmission of a biasing force via spring 119 ontohammer pin 57 has been described hereinbefore. As a further additionalsafety feature, the shear pin ring 113 is dimensioned such that itsupper surface 203 will encounter the bottom shoulder 205 of the pressurebalancing piston 39 and prevent movement of the pressure balancingpiston 39 downwardly sufficiently to impose a force onto the hammer pin57 after the shear pin 117 has been sheared once.

After a normal firing has been completed, the pulling tool is jarredupwardly and the shear up pulling tool then pulls the inverted cone 163from beneath the slip means 141 to disengage the slip means 141 andallow the percussion firing head assembly 11 to be drawn upwardly. Asthe inverted cone 163 is pulled upwardly,

the drag shoe means 139 and the guide pin 143 move downwardly to thelower position 207, FIG. 6. The pulling tool 171, the percussion firinghead assembly 11 and the setting tool 13 are thereafter withdrawn fromthe well. A shear up pulling tool 171 is also employed to allow thepulling tool 171 to be released from the percussion firing head assembly11 in the event one or more of the tools should become immobilized; asby collapsed casing or debris, in conjunction with failure of thesetting tool-13 to shear off of the bridge plug 15. In such as event,the released pulling tool 171 is pulled from the wellbore 25 and astronger pulling apparatus is employed to fish" out the percus sionfiring head assembly 11 and the setting tool 13.

At the surface, the percussion firing head assembly 11 is prepared forsubsequent use by repositioning the respective elements andsubassemblies as illustrated in FIGS. 2-4. Specifically, the hammer pinassembly is reconnected as indicated hereinbefore; that is, by extendingit to its most elongate condition, punching out the parts of shearedshear pin 117 and inserting a new shear pin 117. The pressure balancingpiston 39 is moved'to its uppermost position and the shear pins 115 arereplaced by punching out the parts of sheared shear pins 115 andinserting new shear pins 115. The second housing section 51 is unscrewedfrom the receiver 133 and the ejector cap 131 lifted upwardly, removingthe igniter 127. A new igniter 127 may be emplaced in the ejector cap131 and the tool reassembled as illustrated in FIGS. 24 for anadditional firing run in the same or different wellbore.

Although in the embodiment described and illustrated hereinbefore, asetting tool is shown as the de vice to be actuated responsive to firingof the igniter means 31, it should be understood that the invention maybe used with various such devices; as for example, jet perforating gunsand cut-off tools.

The materials of construction that are ordinarily employed in this artare satisfactory herein and no exotic new materials need be employed.

The percussion firing head assembly 11 is readily adaptable to beconnected with either an internal, FIG. 2, or an external fishing neck,167, FIG. 7. The external fishing neck 167 is connected with theremainder ofthe percussion firing head assembly by conventional means,such as threaded connection 179. When using an outside fishing neck 167,FIG. 7, several options are possible. For example, one can extend theupper end, or upwardly member 59, of the pressure balancing piston to apoint above the fishing neck 167, thereby eliminating the need for aprong 26, per se, FIG. 5, or the side sand drain-off holes, ordownwardly and outwardly extending passageways 69, FIG. 2.

The embodiment of FIG. 7 is run and pulled with conventional externalfishing neck running tools and pulling tools with hollow cores that arepresently available on the market and that need not be described herein.The running, arming and firing, and pulling of the embodiment of FIG. 7are effected substantially as described hereinbefore, except for theapparent difference in the fishing neck structure.

Although the firing has been described hereinbefore by attaching afiring prong 26 onto the bottom ofa pulling tool, or a fishing tool orthe like and employing a wire line tool string, one advantage of thisinvention is that firing can be effected by dropping a bar downwardlythrough conduit in the well-bore, the bar having a similar firing prongattached to its lower end; or by running a similar prong at the bottomend of a macaroni tubing string or the like. When the igniter means 31is fired by macaroni tubing string or pump rod string, the entireassembly can be pulled on the ignition trip or can be fired and thenpulled on a subsequent trip.

Another advantage of this invention is that the percussion firingapparatus may be employed in conjunction with any of the conventionalmeans for suspending it in a well at a predetermined depth; such as,suspending it via a string of tubing or via emplacement on a landingnipple or the like; whether or not such other means are as convenientand as generally available as the example, or embodiment, disclosed.Thereafter, the arming and firing may be effected by an suitable means,such as a second trip with a firing prong or similar prong at the bottomend ofa macaroni tubing string or the like.

From the foregoing descriptive matter, it can be seen that thisinvention provides one or more of the desirable features delineatedhereinbefore and not heretofore provided. In specific embodiments, thisinvention provides all of the desirable features delineatedhereinbefore. While most of the features are believed to beself-explanatory, some of the features and advantages are worthre-iterating. The pressure balancing design of this invention enablesthe percussion firing head assembly to be fired by any of theconventionally employed methods and at any depth, even in viscous fluidsin the wellbore; since firing is responsive to the degree of force alongand not to speed of some falling object, or weight, in the wellbore. Thepressure balancing design prevents adverse effects from either highinternal or external pressures from affecting the downhole arming andfiring sequence. The percussion firing head is set in the wellbore withthe arming means unarmed; and, then, armed and fired on a second tripusing a simple firing prong. Moreover, after a single attempt at firing,the arming means is disarmed for safety. The new balancing piston designof this invention prevents loss of pressure from a pressure operatedtool and thus alleviates difficulties with having tool strings stuck inthe wellbore. Ignition can be accomplished more consistently and easierwith less expensive ignition caps, because there is no necessity forhaving a sealing shear disc to retain the pressures of a connected,pressureoperated tool. Moreover, a consistently repeatable degree ofacceleration of the hammer pin and, hence, a constant load is deliveredto the firing pin for firing regardless of well conditions. Experiencewith experimental models in the field have shown 100 percent firingcompared with only about percent firing for the best comparablenonelectrical prior art type devices. A plurality of safety features areprovided to ensure that there is no subsequent firing in the unlikelyevent there should be a misfire. For example, the firing pin has acontrolled penetration depth so as to obtain ignition but not so greatas to penetrate completely through the head of the igniter 127.Expressed otherwise, even penetration of the thin ignition cap of acenter fire shell is desirable and has not been provided heretofore, butis provided by this invention. In this regard, a cap that had beenmisfired in a surface experimental setup was attempted to be firedrepeatedly, including dropping the entire firing head assembly six timesfrom a height of twelve feet onto concrete without firing the cap. Thisindicates the high degree of safety that is effected as a result of thisfeature. Once a cap is deformed to a maximum depth permitted by thecontrolled depth firing pin without firing, then the same cap cannot befired thereafter by the same firing pin unless the firing pin is allowedto penetrate further. This is a very important secondary feature.

Although this invention has been described with a certain degree ofparticularlity, it is understood that the present disclosure has beenmade only bt way of example and that numerous changes in the details ofconstruction and the combination and arrangement of 5 parts may beresorted to without departing from the spirit and scope of thisinvention.

What is claimed is:

l. Percussion firing apparatus for firing an explosive charge meanswithin a well penetrating subterranean formations comprising:

a. pressure balancing means for neutralizing adverse effects of externalpressure and of internal pressure and changes therein; said pressurebalancing means including a pressure balancing chamber and a pressurebalancing piston that sealingly excludes fluid communication between afiring pin chamber and the exterior of said percussion firing apparatus;

b. a firing pin chamber having therein a firing pin assembly thatincludes:

i. a firing pin disposed within said firing pin assembly; and

ii. arming means disposed intermediate said firing pin and said pressurebalancing chamber and piston such that said firing pin can be forcedsharply downwardly by a downward force on said pressure balancingpiston; said arming means being normally unarmed until after saidpercussion firing apparatus is set in a conduit in said well;

c. igniter means disposed beneath said firing pin so as to be ignitedresponsive to a downwardly moved firing pin;

d. settable hanging means for suspending said percussion firingapparatus in a conduit within said well; said hanging means being set bya downward force and released by an upward force; and

e. first connection means for connection with a device that is actuatedresponsive to the firing of said igniter means.

2. The percussion firing apparatus of claim 1 wherein said arming meansincludes a hammer pin assembly that is disposed intermediate said firingpin and said pressure balancing piston so as to be engaged by saidpressure balancing piston when it is moved downwardly for ignition ofsaid igniter means.

3. The percussion firing apparatus of claim 2 wherein a releasablepiston retainer means is provided; said releasable piston retainer meansholding said pressure balancing piston at a predetermined positionlongitudinally of said pressure balancing chamber and releasing saidpressure balancing piston for downward movement when subjected tosufficient downward force.

4. The percussion firing apparatus of claim 2 wherein there is provideda single-fire safety means interposed intermediate said firing pin andsaid pressure balancing piston; said single-fire safety means allowingarming said hammer pin assembly such that said downward force on saidpressure balancing piston will cause said firing pin to attempt ignitionof said igniter means; said single-fire safety means also effectingdisarming of said hammer pin assembly after one said attempt.

5. The percussion firing apparatus of claim 4 wherein said single-firesafety means comprises a hammer pin; a hammer pin skirt defining a pathdirecting said hammer pin to said firing pin; said hammer pin beingslidably disposed within said hammer pin skirt; and a releasable hammerpin retainer means retaining said hammer pin at the upper portion ofsaid hammer pin skirt prior to attempting ignition of said igniter meansby striking said firing pin with said hammer pin; said releasable hammerpin retainer means releasing said hammer pin for striking said firingpin when subjected to sufficient downward force.

6. The percussion firing apparatus of claim 5 wherein said releasablehammer pin retainer means comprises a shear pin extending laterallythrough said hammer pin skirt and at least into said hammer pin; andsaid hammer pin skirt has a top portion that closely and conforminglyfits the exterior of the bottom of the hammer pin and has an enlargedbore immediately therebelow for preventing any dragging and fluidcompression effects and allowing free and rapid downward movement of thehammer pin once the shear pin has been sheared.

7. The percussion firing apparatus of claim 5 wherein said arming meansincludes a releasable piston retainer means for retaining said pressurebalancing piston in place with respect to said hammer pin prior tomoving downwardly for effecting firing; and includes a biasing meansintermediate said hammer pin said said pressure balancing piston forstoring a predetermined amount of energy for accelerating said hammerpin once said respective releasable piston and hammer pin retainer meanshave been released to ensure that said firing pin is struck sufficientlyhard to effect ignition of said igniter means.

8. The percussion firing apparatus of claim 7 wherein said single-firesafety means includes a shoulder on said hammer pin skirt and a stopring at the lower end of said biasing means for preventing downwardmovement of the lower end of said biasing means beyond said hammer pinskirt whereby downward force on said hammer pin and said firing pincannot be exerted by said biasing means after said single attempt atfiring.

9. The percussion firing apparatus of claim 8 wherein said biasing meanscomprises a spring; and said hammerpin and said shoulder are so designedthat said stop ring encounters said shoulder before said hammer pinencounters said firing pin whereby said hammer pin is accelerated bysaid spring, said spring is prevented from acting upon said hammer pinall the way to said firing pin, and said hammer pin relies upon inertialforce to strike said firing pin with the correct force.

10. The percussion firing apparatus of claim 8 wherein said single-firesafety also includes an exteriorly protruding shoulder on said pressurebalancing piston and an interiorly protruding shoulder for limitingdownward motion of said pressure balancing piston to prevent itsimposing a force on said firing pin by way of said hammer pin after saidreleasable hammer pin retainer means has been released for firing.

11. The percussion firing apparatus of' claim ll wherein said pressurebalancing piston has an upwardly protruding member that is adapted to beacted on for moving said pressure balancing piston downwardly foreffecting arming and firing.

12. The percussion firing apparatus of claim 11 wherein a fishing neckmeans is disposed at the upper end of said percussion firing apparatusand is adapted for being suspended from a shear down wire line runningtool and adapted for being engaged and pulled upwardly by a shear uppulling tool.

13. The percussion firing apparatus of claim 12 wherein said fishingneck means includes an internal fish neck; a housing defines aprong-receiving chamber surrounding said upwardly protruding member onsaid pressure balancing piston; and apertures are provided in saidhousing, said apertures having downwardly and outwardly inclinedsurfaces for draining off trash, debris and the like.

14. The percussion firing apparatus of claim 13 wherein a simpleone-piece prong is included, said prong having a connection means at itsupper end for connection with a pulling tool and being adapted to fitinside said fishingneck means and having its lower end adapted tocontact said upwardly protruding member of said pressure balancingpiston for forcing it downwardly.

15. The percussion firing apparatus of claim 13 wherein said prong andsaid prong-receiving chamber and proportioned such that said pullingtool will have engaged said fishing neck means before said firing pinfires said igniter means responsive to downward pressure of said prong.

16. The percussion firing apparatus of claim 12 wherein said fishingneck means includes an external fish neck and said upwardly protrudingmember on said pressure balancing piston extends above said externalfish neck in the run-in, unarmed position before the arming and firingattempt is made.

17. The percussion firing apparatus of claim 1 wherein said firing pinhas a controlled penetrating depth feature that assures adequatepenetration for ignition but acts as a safety feature in instances whereignition fails to occur.

18. The percussion firing apparatus of claim 17 wherein said controlledpenetrating depth feature includes an enlarged head on said firing pin,said enlarged head having a relatively large flat bottom surface forencountering a second flat surface to limit downward movement thereof;and said firing pin is disposed in an aperture that is surrounded at itsupper end by a second, relatively large, flat surface for stoppingdownward movement of said enlarged head and said firing pin- 19. Thepercussion firing apparatus of claim 1 wherein said pressure balancingpiston is disposed in said pressure balancing chamber; first and secondbores communicate with respective ends of said pressure balancingchamber, said first bore communicating with the exterior of saidpercussion firing apparatus and said second bore communicatinginteriorly thereof with said firing pin chamber; said pressure balancingpiston having an upwardly extending member disposed in said first boreand having a first cross sectional area that is exposed to pressureexteriorly of said percussion firing apparatus; said pressure balancingpiston having a large central portion having a second cross sectionalarea; an aperture communicating with said pressure balancing chambernear its end closest to said second bore and communicating exteriorly ofsaid percussion firing apparatus for exposing the lower portion of saidpressure balancing chamber to pressure exteriorly of said percussionfiring apparatus; said pressure balancing piston having a lower enddisposed in said second bore such that said pressure balancing piston isslidable longitudinally of said first and second bores and said pressurebalancing chamber; said pressure balancing piston having alongitudinally extending internal passageway communicating intermediatesaid second bore and an upper portion of said pressure balancing chamberintermediate said enlarged portion of said pressure balancing piston andsaid first bore for exposing the upper portion of said pressurebalancing chamber to pressure interiorly of said percussion firingapparatus; said lower end of said pressure balancing piston having athird cross sectional area; said second cross sectional area beingenough larger than said first and third cross sectional areas thatpressure interiorly of said percussion firing apparatus will act onexposed said third area and the top exterior portion of said second areaand the pressure exteriorly of said percussion firing apparatus will acton said first area and the bottom exterior portion of said second areato create equal and opposing forces that neutralize each other such thatsaid pressure balancing piston is moved responsive to a force other thanpressure and the effects of pressure are neutralized.

20. The percussion firing apparatus of claim 1 wherein an elongatedetonation passageway is disposed intermediate said igniter means andsaid first connection means for downward passage of the shock wave fromthe ignited igniter means; and wherein a shooting adapter and a boosterpellet are connected with said first connection means and have a thirdconnection means similar to said first connection means for connectingwith a device that is actuated responsive to firing of said boosterpellet.

21. Percussion firing apparatus for firing an explosive charge meanswithin a well penetrating subterranean formations, having means forsuspending a percussion firing head assembly at a predetermined depth,com prising:

a. pressure balancing means for neutralizing adverse effects of externalpressure and ofinternal pressure and changes therein; said pressurebalancing means including a pressure balancing chamber and a pressurebalancing piston that sealingly excludes fluid communication between afiring pin chamber and the exterior of said percussion firing apparatus;

b. a firing pin chamber having therein a firing pin assembly thatincludes:

i. a firing pin disposed within said firing pin assembly; and

ii. arming means disposed intermediate said firing pin and said pressurebalancing chamber and piston such that said firing pin can be forcedsharply downwardly by a downward force on said pressure balancingpiston; said arming means being normally unarmed until after saidpercussion firing apparatus is set in a conduit in said well;

c. igniter means disposed beneath said firing pin so as to be ignitedresponsive to a downwardly moved firing pin; and

d. first connection means for connection with a device that is actuatedresponsive to the firing of said igniter means.

22. The percussion firing apparatus of claim 21 wherein said armingmeans includes a hammer pin assembly that is disposed intermediate saidfiring pin and said pressure balancing piston so as to be engaged bysaid pressure balancing piston when it is moved downwardly for ignitionof said igniter means.

23. The percussion firing apparatus of claim 22 wherein a releasablepiston retainer means is provided; said releasable piston retainer meansholding said pressure balancing piston at a predetermined positionlongitudinally of said pressure balancing chamber and releasing saidpressure balancing piston for downward movement when subjected tosufficient downward force.

24. The percussion firing apparatus of claim 22 wherein there isprovided a single-fire safety means interposed intermediate said firingpin and said pressure balancing piston; said single-fire safety meansallowing arming said hammer pin assembly such that said downward forceon said pressure balancing piston will cause said firing pin to attemptignition of said igniter means; said single-fire safety means alsoeffecting disarming of said hammer pin assembly after one said attempt.

25. The percussion firing apparatus of claim 24 wherein said single-firesafety means comprises a hammer pin; a hammer pin skirt defining a pathdirecting said hammer pin to said firing pin; said hammer pin beingslidably disposed within said hammer pin skirt; and a releasable hammerpin retainer means retaining said hammer pin at the upper portion ofsaid hammer pin skirt prior to attempting ignition of said igniter meansby striking said firing pin with said hammer pin; said releasable hammerpin retainer means releasing said hammer pin for striking saidtfiringpin when subjected to sufficient downward force.

26. The percussion firing apparatus of claim 25 wherein said releasablehammer pin retainer means comprises a shear pin extending laterallythrough said hammer pin skirt and at least into said hammer pin; andsaid hammer pin skirt has a top portion that closely and conforminglyfits the exterior of the bottom of the hammer pin and has an enlargedbore immediately therebelow for preventing any dragging and fluidcompressioneffects and allowing free and rapid downward movement of thehammer pin once the shear pin has been sheared.

27. The percussion firing apparatus of claim 25 wherein said armingmeans includes a releasable piston retainer means for retaining saidpressure balancing piston in place with respect to said hammer pin priorto moving downwardly for effecting firing; and includes a biasing meansintermediate said hammer pin and said pressure balancing piston forstoring a predetermined amount of energy for accelerating said hammerpin once said respective releasable piston and hammer pin retainer meanshave been released to ensure that said firing pin is struck sufficientlyhard to effect ignition of said igniter means.

28. The percussion firing apparatus of claim 27 wherein said single-firesafety means includes a shoulder on said hammer pin skirt and a stopring at the lower end of said biasing means for preventing downwardmovement of the lower end of said biasing means beyond said hammer pinskirt whereby downward force on said hammer pin and said firing pincannot be exerted by said biasing means after said single attempt atfiring.

29. The percussion firing apparatus of claim 28 wherein said biasingmeans comprises a spring; and said hammer pin and said shoulder are sodesigned that said stop ring encounters said shoulder before said hammerpin encounters said firing pin whereby said hammer pin is accelerated bysaid spring, said spring is prevented from acting upon said hammer pinall the way to said firing pin, and said hammer pin relies upon inertialforce to strike said firing pin with the correct force.

30. The percussion firing apparatus of claim 28 wherein said single-firesafety also includes an exteriorly protruding shoulder on said pressurebalancing piston and an interiorly protruding shoulder for limitingdownward motion of said pressure balancing piston to prevent itsimposing a force on said firing pin by way of said hammer pin after saidreleasable hammer pin retainer means has been released for firing.

31. The percussion firing apparatus of claim 21 wherein said pressurebalancing piston has an upwardly protruding member that is adapted to beacted on for moving said pressure balancing piston downwardly foreffecting arming and firing.

32. The percussion firing apparatus of claim 31 wherein a fishing neckmeans is disposed at the upper end of said percussion firing apparatusand is adapted for being suspended from a tubing string for emplacementin and removal from said well.

33. The percussion firing apparatus of claim 32 wherein said fishingneck means includes an internal fish neck; a housing defines aprong-receiving chamber surrounding said upwardly protruding member onsaid pressure balancing piston; and apertures are provided in saidhousing, said apertures having downwardly and outwardly inclinedsurfaces for draining off trash, debris and the like.

34. The percussion firing apparatus of claim 33 wherein a simpleone-piece prong is included, said prong having a connection means at itsupper end for connection with a means for imposing a downward force;said prong being adapted to fit inside said fishing neck means andhaving its lower end adapted to contact said upwardly protruding memberof said pressure balancing piston for forcing it downwardly.

35. The percussion firing apparatus of claim 21 wherein said firing pinhas a controlled penetrating depth feature that assures adequatepenetration for ignition but acts as a safety feature in instances whereignition fails to occur.

36. The percussion firing apparatus of claim 35 wherein said controlledpenetrating depth feature includes an enlarged head on said firing pin,said enlarged head having a relatively large flat bottom surface forencountering a second flat surface to limit downward movement thereof;and said firing pin is disposed in an aperture that is surrounded at itsupper end by a second, relatively large, flat surface for stoppingdownward movement of said enlarged head and said firing pin.

37. The percussion firing apparatus of claim 21 wherein said pressurebalancing piston is disposed in said pressure balancing chamber; firstand second bores communicate with respective ends of said pressurebalancing chamber, said first bore communicating with the exterior ofsaid percussion firing apparatus and said second bore communicatinginteriorly thereof with said firing pin chamber; said pressure balancingpiston having an upwardly extending member disposed in said first boreand having a first cross sectional area that is exposed to pressureexteriorly of said percussion firing apparatus; said pressure balancingpiston having a large central portion having a second cross sectionalarea; an aperture communicating with said pressure balancing chambernear its end closest to said second bore and communicating exteriorly ofsaid percussion firing apparatus for exposing the lower portion of saidpressure balancing chamber to pressure exteriorly of said percussionfiring apparatus; said pressure balancing piston having a lower enddisposed in said second bore such that said pressure balancing piston isslidable longitudinally of said first and second bores and said pressurebalancing chamber; said pressure balancing piston having alongitudinally extending internal passageway communicating intermediatesaid second bore and an upper portion of said pressure balancing chamberintermediate said enlarged portion of said pressure balancing piston andsaid first bore for exposing the upper portion of said pressurebalancing chamber to pressure interiorly of said percussion firingapparatus; said lower end of said pressure balancing piston having athird cross sectional area; said second cross sectional area beingenough larger than said first and third cross sectional areas thatpressure interiorly of said percussion firing apparatus will act onexposed said third area and the top exterior portion of said second areaand the pressure exteriorly of said percussion firing apparatus will acton said first area and the bottom exterior portion of said second areato create equal and opposing forces that neutralize each other such thatsaid pressure balancing piston is moved responsive to a force other thanpressure and the effects of pressure are neutralized.

38. The percussion firing apparatus of claim 21 wherein an elongatedetonation passageway is disposed intermediate said igniter means andsaid first connection means for downward passage of the shock wave fromthe ignited igniter means; and wherein a shooting adapter and a boosterpellet are connected with said first connection means and have a thirdconnection means similar to said first'connection means for'con nectingwith a device that is actuated responsive to firing of said boosterpellet.

1. Percussion firing apparatus for firing an explosive charge meanswithin a well penetrating subterranean formations comprising: a.pressure balancing means for neutralizing adverse effects of externalpressure and of internal pressure and changes therein; said pressurebalancing means including a pressure balancing chamber and a pressurebalancing piston that sealingly excludes fluid communication between afiring pin chamber and the exterior of said percussion firing apparatus;b. a firing pin chamber having therein a firing pin assembly thatincludes: i. a firing pin disposed within said firing pin assembly; andii. arming means disposed intermediate said firing pin and said pressurebalancing chamber and piston such that said firing pin can be forcedsharply downwardly by a downward force on said pressure balancingpiston; said arming means being normally unarmed until after saidpercussion firing apparatus is set in a conduit in said well; c. ignitermeans disposed beneath said firing pin so as to be ignited responsive toa downwardly moved firing pin; d. settable hanging means for suspendingsaid percussion firing apparatus in a conduit within said well; saidhanging means being set by a downward force and released by an upwardforce; and e. first connection means for connection with a device thatis actuated responsive to the firing of said igniter means.
 2. Thepercussion firing apparatus of claim 1 wherein said arming meansincludes a hammer pin assembly that is Disposed intermediate said firingpin and said pressure balancing piston so as to be engaged by saidpressure balancing piston when it is moved downwardly for ignition ofsaid igniter means.
 3. The percussion firing apparatus of claim 2wherein a releasable piston retainer means is provided; said releasablepiston retainer means holding said pressure balancing piston at apredetermined position longitudinally of said pressure balancing chamberand releasing said pressure balancing piston for downward movement whensubjected to sufficient downward force.
 4. The percussion firingapparatus of claim 2 wherein there is provided a single-fire safetymeans interposed intermediate said firing pin and said pressurebalancing piston; said single-fire safety means allowing arming saidhammer pin assembly such that said downward force on said pressurebalancing piston will cause said firing pin to attempt ignition of saidigniter means; said single-fire safety means also effecting disarming ofsaid hammer pin assembly after one said attempt.
 5. The percussionfiring apparatus of claim 4 wherein said single-fire safety meanscomprises a hammer pin; a hammer pin skirt defining a path directingsaid hammer pin to said firing pin; said hammer pin being slidablydisposed within said hammer pin skirt; and a releasable hammer pinretainer means retaining said hammer pin at the upper portion of saidhammer pin skirt prior to attempting ignition of said igniter means bystriking said firing pin with said hammer pin; said releasable hammerpin retainer means releasing said hammer pin for striking said firingpin when subjected to sufficient downward force.
 6. The percussionfiring apparatus of claim 5 wherein said releasable hammer pin retainermeans comprises a shear pin extending laterally through said hammer pinskirt and at least into said hammer pin; and said hammer pin skirt has atop portion that closely and conformingly fits the exterior of thebottom of the hammer pin and has an enlarged bore immediately therebelowfor preventing any dragging and fluid compression effects and allowingfree and rapid downward movement of the hammer pin once the shear pinhas been sheared.
 7. The percussion firing apparatus of claim 5 whereinsaid arming means includes a releasable piston retainer means forretaining said pressure balancing piston in place with respect to saidhammer pin prior to moving downwardly for effecting firing; and includesa biasing means intermediate said hammer pin said said pressurebalancing piston for storing a predetermined amount of energy foraccelerating said hammer pin once said respective releasable piston andhammer pin retainer means have been released to ensure that said firingpin is struck sufficiently hard to effect ignition of said ignitermeans.
 8. The percussion firing apparatus of claim 7 wherein saidsingle-fire safety means includes a shoulder on said hammer pin skirtand a stop ring at the lower end of said biasing means for preventingdownward movement of the lower end of said biasing means beyond saidhammer pin skirt whereby downward force on said hammer pin and saidfiring pin cannot be exerted by said biasing means after said singleattempt at firing.
 9. The percussion firing apparatus of claim 8 whereinsaid biasing means comprises a spring; and said hammer pin and saidshoulder are so designed that said stop ring encounters said shoulderbefore said hammer pin encounters said firing pin whereby said hammerpin is accelerated by said spring, said spring is prevented from actingupon said hammer pin all the way to said firing pin, and said hammer pinrelies upon inertial force to strike said firing pin with the correctforce.
 10. The percussion firing apparatus of claim 8 wherein saidsingle-fire safety also includes an exteriorly protruding shoulder onsaid pressure balancing piston and an interiorly protruding shoulder forlimiting downward motion of said pressure balancing piston to preventits imposing a force on saiD firing pin by way of said hammer pin aftersaid releasable hammer pin retainer means has been released for firing.11. The percussion firing apparatus of claim 1 wherein said pressurebalancing piston has an upwardly protruding member that is adapted to beacted on for moving said pressure balancing piston downwardly foreffecting arming and firing.
 12. The percussion firing apparatus ofclaim 11 wherein a fishing neck means is disposed at the upper end ofsaid percussion firing apparatus and is adapted for being suspended froma ''''shear down'''' wire line running tool and adapted for beingengaged and pulled upwardly by a ''''shear up'''' pulling tool.
 13. Thepercussion firing apparatus of claim 12 wherein said fishing neck meansincludes an internal fish neck; a housing defines a prong-receivingchamber surrounding said upwardly protruding member on said pressurebalancing piston; and apertures are provided in said housing, saidapertures having downwardly and outwardly inclined surfaces for drainingoff trash, debris and the like.
 14. The percussion firing apparatus ofclaim 13 wherein a simple one-piece prong is included, said prong havinga connection means at its upper end for connection with a pulling tooland being adapted to fit inside said fishing neck means and having itslower end adapted to contact said upwardly protruding member of saidpressure balancing piston for forcing it downwardly.
 15. The percussionfiring apparatus of claim 13 wherein said prong and said prong-receivingchamber and proportioned such that said pulling tool will have engagedsaid fishing neck means before said firing pin fires said igniter meansresponsive to downward pressure of said prong.
 16. The percussion firingapparatus of claim 12 wherein said fishing neck means includes anexternal fish neck and said upwardly protruding member on said pressurebalancing piston extends above said external fish neck in the run-in,unarmed position before the arming and firing attempt is made.
 17. Thepercussion firing apparatus of claim 1 wherein said firing pin has acontrolled penetrating depth feature that assures adequate penetrationfor ignition but acts as a safety feature in instances where ignitionfails to occur.
 18. The percussion firing apparatus of claim 17 whereinsaid controlled penetrating depth feature includes an enlarged head onsaid firing pin, said enlarged head having a relatively large flatbottom surface for encountering a second flat surface to limit downwardmovement thereof; and said firing pin is disposed in an aperture that issurrounded at its upper end by a second, relatively large, flat surfacefor stopping downward movement of said enlarged head and said firingpin.
 19. The percussion firing apparatus of claim 1 wherein saidpressure balancing piston is disposed in said pressure balancingchamber; first and second bores communicate with respective ends of saidpressure balancing chamber, said first bore communicating with theexterior of said percussion firing apparatus and said second borecommunicating interiorly thereof with said firing pin chamber; saidpressure balancing piston having an upwardly extending member disposedin said first bore and having a first cross sectional area that isexposed to pressure exteriorly of said percussion firing apparatus; saidpressure balancing piston having a large central portion having a secondcross sectional area; an aperture communicating with said pressurebalancing chamber near its end closest to said second bore andcommunicating exteriorly of said percussion firing apparatus forexposing the lower portion of said pressure balancing chamber topressure exteriorly of said percussion firing apparatus; said pressurebalancing piston having a lower end disposed in said second bore suchthat said pressure balancing piston is slidable longitudinally of saidfirst and second bores and said pressure balancing chamber; saidpressure balancing piston having a longitudinally extending internalPassageway communicating intermediate said second bore and an upperportion of said pressure balancing chamber intermediate said enlargedportion of said pressure balancing piston and said first bore forexposing the upper portion of said pressure balancing chamber topressure interiorly of said percussion firing apparatus; said lower endof said pressure balancing piston having a third cross sectional area;said second cross sectional area being enough larger than said first andthird cross sectional areas that pressure interiorly of said percussionfiring apparatus will act on exposed said third area and the topexterior portion of said second area and the pressure exteriorly of saidpercussion firing apparatus will act on said first area and the bottomexterior portion of said second area to create equal and opposing forcesthat neutralize each other such that said pressure balancing piston ismoved responsive to a force other than pressure and the effects ofpressure are neutralized.
 20. The percussion firing apparatus of claim 1wherein an elongate detonation passageway is disposed intermediate saidigniter means and said first connection means for downward passage ofthe shock wave from the ignited igniter means; and wherein a shootingadapter and a booster pellet are connected with said first connectionmeans and have a third connection means similar to said first connectionmeans for connecting with a device that is actuated responsive to firingof said booster pellet.
 21. Percussion firing apparatus for firing anexplosive charge means within a well penetrating subterraneanformations, having means for suspending a percussion firing headassembly at a predetermined depth, comprising: a. pressure balancingmeans for neutralizing adverse effects of external pressure and ofinternal pressure and changes therein; said pressure balancing meansincluding a pressure balancing chamber and a pressure balancing pistonthat sealingly excludes fluid communication between a firing pin chamberand the exterior of said percussion firing apparatus; b. a firing pinchamber having therein a firing pin assembly that includes: i. a firingpin disposed within said firing pin assembly; and ii. arming meansdisposed intermediate said firing pin and said pressure balancingchamber and piston such that said firing pin can be forced sharplydownwardly by a downward force on said pressure balancing piston; saidarming means being normally unarmed until after said percussion firingapparatus is set in a conduit in said well; c. igniter means disposedbeneath said firing pin so as to be ignited responsive to a downwardlymoved firing pin; and d. first connection means for connection with adevice that is actuated responsive to the firing of said igniter means.22. The percussion firing apparatus of claim 21 wherein said armingmeans includes a hammer pin assembly that is disposed intermediate saidfiring pin and said pressure balancing piston so as to be engaged bysaid pressure balancing piston when it is moved downwardly for ignitionof said igniter means.
 23. The percussion firing apparatus of claim 22wherein a releasable piston retainer means is provided; said releasablepiston retainer means holding said pressure balancing piston at apredetermined position longitudinally of said pressure balancing chamberand releasing said pressure balancing piston for downward movement whensubjected to sufficient downward force.
 24. The percussion firingapparatus of claim 22 wherein there is provided a single-fire safetymeans interposed intermediate said firing pin and said pressurebalancing piston; said single-fire safety means allowing arming saidhammer pin assembly such that said downward force on said pressurebalancing piston will cause said firing pin to attempt ignition of saidigniter means; said single-fire safety means also effecting disarming ofsaid hammer pin assembly after one said attempt.
 25. The percussionfiring apparatus of Claim 24 wherein said single-fire safety meanscomprises a hammer pin; a hammer pin skirt defining a path directingsaid hammer pin to said firing pin; said hammer pin being slidablydisposed within said hammer pin skirt; and a releasable hammer pinretainer means retaining said hammer pin at the upper portion of saidhammer pin skirt prior to attempting ignition of said igniter means bystriking said firing pin with said hammer pin; said releasable hammerpin retainer means releasing said hammer pin for striking said firingpin when subjected to sufficient downward force.
 26. The percussionfiring apparatus of claim 25 wherein said releasable hammer pin retainermeans comprises a shear pin extending laterally through said hammer pinskirt and at least into said hammer pin; and said hammer pin skirt has atop portion that closely and conformingly fits the exterior of thebottom of the hammer pin and has an enlarged bore immediately therebelowfor preventing any dragging and fluid compression effects and allowingfree and rapid downward movement of the hammer pin once the shear pinhas been sheared.
 27. The percussion firing apparatus of claim 25wherein said arming means includes a releasable piston retainer meansfor retaining said pressure balancing piston in place with respect tosaid hammer pin prior to moving downwardly for effecting firing; andincludes a biasing means intermediate said hammer pin and said pressurebalancing piston for storing a predetermined amount of energy foraccelerating said hammer pin once said respective releasable piston andhammer pin retainer means have been released to ensure that said firingpin is struck sufficiently hard to effect ignition of said ignitermeans.
 28. The percussion firing apparatus of claim 27 wherein saidsingle-fire safety means includes a shoulder on said hammer pin skirtand a stop ring at the lower end of said biasing means for preventingdownward movement of the lower end of said biasing means beyond saidhammer pin skirt whereby downward force on said hammer pin and saidfiring pin cannot be exerted by said biasing means after said singleattempt at firing.
 29. The percussion firing apparatus of claim 28wherein said biasing means comprises a spring; and said hammer pin andsaid shoulder are so designed that said stop ring encounters saidshoulder before said hammer pin encounters said firing pin whereby saidhammer pin is accelerated by said spring, said spring is prevented fromacting upon said hammer pin all the way to said firing pin, and saidhammer pin relies upon inertial force to strike said firing pin with thecorrect force.
 30. The percussion firing apparatus of claim 28 whereinsaid single-fire safety also includes an exteriorly protruding shoulderon said pressure balancing piston and an interiorly protruding shoulderfor limiting downward motion of said pressure balancing piston toprevent its imposing a force on said firing pin by way of said hammerpin after said releasable hammer pin retaIner means has been releasedfor firing.
 31. The percussion firing apparatus of claim 21 wherein saidpressure balancing piston has an upwardly protruding member that isadapted to be acted on for moving said pressure balancing pistondownwardly for effecting arming and firing.
 32. The percussion firingapparatus of claim 31 wherein a fishing neck means is disposed at theupper end of said percussion firing apparatus and is adapted for beingsuspended from a tubing string for emplacement in and removal from saidwell.
 33. The percussion firing apparatus of claim 32 wherein saidfishing neck means includes an internal fish neck; a housing defines aprong-receiving chamber surrounding said upwardly protruding member onsaid pressure balancing piston; and apertures are provided in saidhousing, said apertures having downwardly and outwardly inclinedsurfaces for draining off trash, debris and the like.
 34. The percussionfiring apparatus of claim 33 wherein a simple one-piece prong isincluDed, said prong having a connection means at its upper end forconnection with a means for imposing a downward force; said prong beingadapted to fit inside said fishing neck means and having its lower endadapted to contact said upwardly protruding member of said pressurebalancing piston for forcing it downwardly.
 35. The percussion firingapparatus of claim 21 wherein said firing pin has a controlledpenetrating depth feature that assures adequate penetration for ignitionbut acts as a safety feature in instances where ignition fails to occur.36. The percussion firing apparatus of claim 35 wherein said controlledpenetrating depth feature includes an enlarged head on said firing pin,said enlarged head having a relatively large flat bottom surface forencountering a second flat surface to limit downward movement thereof;and said firing pin is disposed in an aperture that is surrounded at itsupper end by a second, relatively large, flat surface for stoppingdownward movement of said enlarged head and said firing pin.
 37. Thepercussion firing apparatus of claim 21 wherein said pressure balancingpiston is disposed in said pressure balancing chamber; first and secondbores communicate with respective ends of said pressure balancingchamber, said first bore communicating with the exterior of saidpercussion firing apparatus and said second bore communicatinginteriorly thereof with said firing pin chamber; said pressure balancingpiston having an upwardly extending member disposed in said first boreand having a first cross sectional area that is exposed to pressureexteriorly of said percussion firing apparatus; said pressure balancingpiston having a large central portion having a second cross sectionalarea; an aperture communicating with said pressure balancing chambernear its end closest to said second bore and communicating exteriorly ofsaid percussion firing apparatus for exposing the lower portion of saidpressure balancing chamber to pressure exteriorly of said percussionfiring apparatus; said pressure balancing piston having a lower enddisposed in said second bore such that said pressure balancing piston isslidable longitudinally of said first and second bores and said pressurebalancing chamber; said pressure balancing piston having alongitudinally extending internal passageway communicating intermediatesaid second bore and an upper portion of said pressure balancing chamberintermediate said enlarged portion of said pressure balancing piston andsaid first bore for exposing the upper portion of said pressurebalancing chamber to pressure interiorly of said percussion firingapparatus; said lower end of said pressure balancing piston having athird cross sectional area; said second cross sectional area beingenough larger than said first and third cross sectional areas thatpressure interiorly of said percussion firing apparatus will act onexposed said third area and the top exterior portion of said second areaand the pressure exteriorly of said percussion firing apparatus will acton said first area and the bottom exterior portion of said second areato create equal and opposing forces that neutralize each other such thatsaid pressure balancing piston is moved responsive to a force other thanpressure and the effects of pressure are neutralized.
 38. The percussionfiring apparatus of claim 21 wherein an elongate detonation passagewayis disposed intermediate said igniter means and said first connectionmeans for downward passage of the shock wave from the ignited ignitermeans; and wherein a shooting adapter and a booster pellet are connectedwith said first connection means and have a third connection meanssimilar to said first connection means for connecting with a device thatis actuated responsive to firing of said booster pellet.